1. Field of the Invention
The invention is concerned with a chevron device limiting mill discharge in a fluid bed system which receives material in a coarse condition and reduce the material to a substantial uniform size dictated by the chevron device for subsequent use.
2. Description of the Prior Art
In the field of the invention apparatus is known to be able to pulverize material in a constant ventilation system so that material particles are released for collection when they reach a required degree of fineness. Such apparatus is disclosed in U.S. Pat. No. 1,583,429 of May 4, 1926. This apparatus was followed by a forced circulation material classifier having a rotary mill having flat blades for pulverizing material, as shown in U.S. Pat. No. 2,931,581 of Apr. 5, 1960. In this type of apparatus the reduced material is delivered out of the closed mill through a venturi throat by fan action as in U.S. Pat. No. 4,566,639 of Jan. 28, 1986.
In later material reduction apparatus having impact hammer rotors, the material to be reduced enters into a closed hammer rotor chamber through a venturi which functions both as an inlet for material to be reduced and as an outlet for the reduced material. Such apparatus is known in U.S. Pat. Nos. 3,794,251 of Feb. 26, 1974 and U.S. Pat. No. 3,826,208 of Jul. 30, 1974.
Further types of apparatus operate to extract hard to grind material from the fractions that are reduced to a fineness of useful size, as in U.S. Pat. No. 4,498,633 of Feb. 12, 1985. In this class of apparatus there is disclosed an impact mill for processing two different types of material and forming a bed of material in the bottom of the mill chamber to collect material that is relatively soft to minimize the production of fines in the outgoing material from the mill of U.S. Pat. No. 4,641,788 of Feb. 10, 1987.
The problem in the apparatus of the prior art is that where a rotary hammer mill is employed the larger and/or heavier particles of the material being processed for reduction fly off the hammers at a velocity approaching the tip speed of the mill hammers and this improperly sized material gets into the stream of properly reduced material. Such larger and/or heavier particles act also with a force in which damage can result. A further problem with the prior art apparatus is that the air moving fan devices when located in the outlets are not protected from being impacted by the fractions of the harder and heavier material thrown out by the mill hammers.